1) Field of the Invention
The present invention relates to a color printer which is connected to an upper unit such as a host computer to perform a printing operation according to data from the upper unit.
2) Description of the Related Art
Generally, as shown in FIG. 22, a color printer 100 is connected to a host computer 110 acting as an upper unit. The color printer 100 receives data from the host computer 110 and then performs a color printing on a predetermined sheet.
The printer 100 generally consists of a color-print mechanical engine 101, a double-sided surface mechanism unit 102, hoppers 103 and 104, a cassette 105, a tray 106, a stacker 107, and an operator panel 108.
The color-print mechanical engine 101 is a mechanism which performs a color printing operation on a predetermined sheet. The double-sided surface mechanism unit 102 is a mechanism which reverses a predetermined sheet to perform a double-sided printing on it.
The hoppers 103 and 104 each store ordinary paper of a predetermined size as print sheets. The cassette 105 stores color sheets each which is fed, prior to shifting to the next job print and after a completion of a job print, to divide the job printing operation. The tray 106 and the stacker 107 each serves as a printed sheet ejecting device.
Moreover, the operator panel 108 includes a control key, switches, and others used for inputting various instructions to the printer 100 as well as a display unit which displays the operation state of the printer 100. Referring to FIG. 22, numeral 111 represents a main console arranged to the host computer 110. The main console 111 includes a control key, switches, a display unit, and others to intervene or monitor the operation of the host computer 110 according to operator's requests.
As shown in FIG. 23, the color-print mechanical engine 101 includes four color printing units 111Y, 111M, 111C and 111K. The color printing unit 111Y prints in yellow (Y) color. The color printing unit 111M prints in magenta (M) color. The color printing unit 111C prints in cyan (C) color. The color printing unit 111K prints in black (K) color. Each color printing unit includes a developing unit 112, a photosensitive body (transfer drum) 113, an optical unit 114, and a transfer roller 115.
The elements 112 to 115 constituting each of the color printing units 111Y, 111M, 111C and 111K are very general. Hence, the detail explanation will be omitted here.
Numeral 116 represents a fixing unit and 117 represents a sheet conveying path.
In the color-print mechanical engine 101 with the configuration shown in FIG. 23, when a sheet fed out of the hopper 103 or 104 is fed from the color printing unit 111Y to the color printing unit 111K along the sheet conveying path 117, color printing units 111Y, 111M, 111C and 111K transfer respectively a color toner onto the sheet. Then a color printing is made by fixing the transferred toner on the sheet by means of the fixing unit 116.
In such a case, when the color printer 100 including the color printing units 111Y, 111M, 111C and 111K performs a monochrome printing, all the color printing units 111Y, 111M, 111C and 111K are always operating. Hence the photosensitive body (transfer drum) 113 of the color printing unit with less use frequency is wasted and the developing solution used in the color printing unit is deteriorated. Moreover, the color printer has a disadvantage of reducing the serviceable life of the color printing unit with a low use frequency.
Moreover, there is a disadvantage in that operating simultaneously the unused color printing unit wastes power consumption and results in a deteriorated print quality because the toner left on the photosensitive body (transfer drum) 113 of unused color printing unit adheres on the sheet and becomes a stain.
For that reason, in order to prolong the serviceable life of a color printing unit with a low use frequency, it may be considered that the power consumption is decreased by performing the evacuation/return operation of each color printing unit, in which a color printing unit not used is put into an evacuation state in advance, not directly in contact with a print sheet, (referred to as an evacuation operation) and then the color printing unit in the evacuation state is set in a return state (referred to as a return operation) in which printing is performed on a print sheet when printing is performed with the color printing unit, for each print page by using color information of print data.
The evacuation/return operation of each color printing unit is mechanically motorized with the printing operation ceased. Hence there is a disadvantage in that the evacuation/return operation of each color printing unit for each print page takes much time, thus degrading the printing performance.